Windows of this type are known in connection with X-ray tubes, i.e. high vacuum tubes, serving as the source of radiation, in order to permit the X-rays produced in such tubes to be transmitted through the vacuum-tight wall with as little loss as possible. Windows permitting such passage are also needed in connection with tubes in which X-rays, or similar penetrating radiation of isotopes such as, for example, gamma rays, are to be converted into signals for further registration. Such tubes, in particular, must be vacuum-tight if conversion into electrons is intended, or if the converting elements such as, for example, photoelectric cathodes containing alkali metals, are sensitive to atmospheric influences. Tubes of this type may, for example, contain measuring probes for producing electrical measuring signals, or they may contain apparatus suitable for converting the rays into optical or electrical signals, from which a visible image may then be obtained. Such tubes are known, for example, as picture-forming or image-converting tubes, television tubes and the like.
The known tubes comprise metal windows which permit X-rays, gamma rays and the like to be passed through such windows. Such windows are therefore often composed of beryllium (Be) which is rather permeable to such rays. These known beryllium window plates are combined with the housing or shell of the tube by means of soldering or welding, including the use of an intermediate arrangement of connecting elements (see U.S. Pat. No. 3,419,741, and British Pat. No. 978 878). However, in the present state of the art, beryllium window plates are not available in any size or shape. Moreover, the shaping of beryllium poses many problems. However, for many purposes of the application of X-ray windows, for example, for use in X-ray picture amplifiers, a large diameter and freedom of shaping limitations are needed in addition to the availability of an economically justifiable material. It is for this reason that in vacuum picture amplifiers, the windows are currently still prepared from glass, although this material absorbs X-rays to a substantial extent.
It has also been attempted to use thin foils of titanium as the material of windows permitting the passage of radiation (see U.S. Pat. No. 3,878,417). The problem of securing these thin foils is resolved by enclosing the metal foil in a stable frame which, for example, may be prepared from steel. Such a frame has the shape of a ring; the marginal portions of the ring, or frame, and the ones of the foil are fused together. However, if vacuum tubes are used, the thin foil is sucked into the inner space of the chamber, which makes it necessary to design the chamber with lengths greater than those usually provided for outwardly curved windows for image amplifiers.
It was also not possible to successfully employ foils which were entirely made of aluminum, thus of a light metal, or alloy. No satisfying way was hitherto found in which electric transmissions could be conducted through a wall of aluminum in a manner that would be accesptable in practical applications.
It is known also to weld disks of light metal into a heavy metal frame, whereby it is possible to obtain in a simple manner disks even with large diameters, which may then be shaped or formed in any desired way (see U.S. Pat. Application 607,874). This method comprises the use of a disk composed of light metals or alloys other than beryllium, and coating or cladding the light metal along its marginal edges with a fusible heavy material, which coating or cladding is subsequently fused tight with the frame. One of the embodiments of the above type comprises fitting the edges of the window plate axially and outwardly flanged into a ring-shaped frame, and subsequently fusing together the edges of the tubular flange and the tubular frame.
When studying the problem here in question, it was found that it may be advantageous if the window plates could be secured without involving a heating step, i.e. without the heating required in a welding or soldering operation. For example, by not using any additional agents such as, for example, solder or adhesive, it could perhaps be avoided that fluxing agents or binders and hardening agents would later give off gas and be damaging to the high vacuum.